`A B C D` is a parallelogram and `O` is any point in its interior. Prove that: <br> (i) `a r\ ( A O B)+a r\ (C O D)=1/2\ a r(A B C D)`  <br> (ii) `a r\ ( A O B)+\ a r\ ( C O D)=\ a r\ ( B O C)+\ a r( A O D)`
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